World powers have agreed to seek a nationwide “cessation of hostilities” in Syria to begin in a week’s time, after talks in Germany.
The halt will not apply to the battle against jihadist groups Islamic State (IS) and al-Nusra Front.
Ministers from the International Syria Support Group also agreed to accelerate and expand aid deliveries.
The announcement comes as the Syrian army, backed by Russian air strikes, advances in Aleppo province.
The move threatens to encircle tens of thousands of civilians in rebel-held parts of the major city of Aleppo.
US Secretary of State John Kerry admitted the ceasefire plan was “ambitious” and said the real test would be whether the parties honoured the commitments.
“What we have here are words on paper, what we need to see in the next few days are actions on the ground,” he said.
A task force chaired by the US and Russia will work to implement the truce through consultations with Syria’s warring factions.
Aid deliveries for besieged Syrian communities are due to begin as early as Friday.